Add some guidelines for PRs
Add some guidelines for PRs

willsALMANJ/vimium,Aleroniponi/vimium,elderbas/vimium,hhsue/vimium,poacher2k/vimium,PickRelated/vimium,poacher2k/vimium,justalittlenoob/vimium,mrmr1993/vimium,douglas-larocca/vimium,crazypenguincode/vimium,bkudria/vimium,justalittlenoob/vimium,Robinson10240/vimium,hhsue/vimium,douglas-larocca/vimium,cyrixhero/vimium,mrmr1993/vimium,philc/vimium,PickRelated/vimium,crazypenguincode/vimium,willsALMANJ/vimium,cyrixhero/vimium,wildeyes/vimium,tuchangwei/vimium,gdh1995/vimium,smblott-github/vimium,Robinson10240/vimium,borgified/vimium,PrestanceDesign/vimium,elegantwww/vimium,VPashkov/vimium,dimatter/vimium,gdh1995/vimium,zhangmin510/vimium,borgified/vimium,elderbas/vimium,gdh1995/vimium,cyrixhero/vimium,dimatter/vimium,decaffeinate-examples/vimium,Robinson10240/vimium,decaffeinate-examples/vimium,bkudria/vimium,dimatter/vimium,borgified/vimium,Lw-Cui/vimium,smblott-github/vimium,willsALMANJ/vimium,Aleroniponi/vimium,tuchangwei/vimium,poacher2k/vimium,csmalin/vimium,Lw-Cui/vimium,decaffeinate-examples/vimium,tuchangwei/vimium,PrestanceDesign/vimium,douglas-larocca/vimium,Lw-Cui/vimium,csmalin/vimium,zhangmin510/vimium,philc/vimium,Aleroniponi/vimium,elderbas/vimium,hhsue/vimium,elegantwww/vimium,PickRelated/vimium,philc/vimium,PrestanceDesign/vimium,zhangmin510/vimium,wildeyes/vimium,VPashkov/vimium,csmalin/vimium,wildeyes/vimium,bkudria/vimium,elegantwww/vimium,smblott-github/vimium,justalittlenoob/vimium,mrmr1993/vimium,VPashkov/vimium